Determining the exact generator size required to safely run a welding machine is not always a straightforward process. Some of the factors to be considered are: the current draw ratings of the welder, the rated output of the generator and whether the generator will or will not be used to run other power equipment at the same time.

Generator size needed for common welder sizes are

Welder with output up to 160A

The optimal generator size would be 8+kva .The minimum size of generator that can be used is 7kva.

Welder with output from 180A to 200A

The optimal size of generator for this type of output is 10+kva. The miminum size of generator suitable for the welder is 8kva.

Welder with maximum output of 250A

The optimal generator size for these welders is 15+kva. The minimum suitable generator size for such welders is 13kva.

Note that if it is intended that the generator will be used to run additional equipment at the same time as the welder, the size of the generator should be increased accordingly. These figures are an approximate guide only and should not replace manufacturers recommendations.

'Minimum' size is the smallest that we suggest to minimize risk if voltage spikes etc, however it may not be enough to achieve full output from the welder.

Optimal’ size will further minimize risk of power supply issues and will allow a higher output from the welder.

Generator for an inverter welder?

If the welder in question is an Inverter Welder, with wattage less than 3000W, the 3000W generator will not run it.

Without a doubt, this contradicts the principle of welders requiring equal or slightly higher wattage generators. As an inverter welder will require a generator that produces at least 1.5 times more power.

Thus, an ideal generator for any inverter welder is the one with wattage 1.5 times higher than the required input voltage.

The difference in the quality of mains and generator power

Power supply from the mains

The power supply from the AC mains is devoid of fluctuations. The voltage is constant without any rise or sudden peaks. It is safe for all kinds of power tools and welders. It enables any welder to perform smoothly and safeguards against circuit breaks and overloading.

Power supply from the generators

Power supply from the portable generators can fluctuate with surges and spikes. This, without a doubt, can be harmful to welders. The sudden rise and fall in voltage can adversely affect the performance and functioning of the welder. It is increasing the chances of overloading and circuit breaks. An AVR controlled generator is recommended as they have less fluctuations with their output.